Nagrani S, Bisby R H
Department of Biological Sciences, University of Salford, U.K.
Int J Radiat Biol. 1989 Feb;55(2):191-200. doi: 10.1080/09553008914550241.
The inactivation of external yeast invertase by irradiation in dilute aqueous solution has been investigated. The contributions of the individual radical species from water radiolysis to inactivation and amino acid degradation were estimated from the results of experiments in which solutions were saturated with nitrogen, nitrous oxide or oxygen, and on addition of hydroxyl radical scavengers. Under conditions where inactivation by hydroxyl radicals predominates, the rate of inactivation increased with increasing dose, indicating that in the initial stages of the radiolysis the mannose-rich oligosaccharide chains of the glycoprotein protect the polypeptide chain from radical attack. Amino acid analysis of the irradiated external invertase showed that there was significant destruction of tyrosine, phenylalanine, methionine and histidine residues. Destruction of methionine and histidine residues may be responsible for the free radical-induced inactivation of this enzyme.
已对稀水溶液中辐照使外源酵母转化酶失活的情况进行了研究。根据在溶液用氮气、一氧化二氮或氧气饱和以及添加羟基自由基清除剂的实验结果，估算了水辐解产生的各个自由基物种对失活和氨基酸降解的贡献。在羟基自由基主导失活的条件下，失活速率随剂量增加而增加，这表明在辐解的初始阶段，糖蛋白中富含甘露糖的寡糖链可保护多肽链免受自由基攻击。对辐照后的外源转化酶进行氨基酸分析表明，酪氨酸、苯丙氨酸、蛋氨酸和组氨酸残基有显著破坏。蛋氨酸和组氨酸残基的破坏可能是该酶自由基诱导失活的原因。
